Concrete blocks have been a basic building material for many years. Concrete blocks have been designed for use in many applications, including concrete masonry blocks used in the construction of foundations of residential and commercial buildings, as well as in constructing the interior and exterior walls of such buildings, and concrete retaining wall blocks used to construct retaining walls. Concrete masonry blocks are typically laid up in courses with mortar being used to secure the blocks to one another, while concrete retaining wall blocks are typically dry stacked in ascending courses without the use of mortar.
One example of a concrete masonry block is the well known gray building block. A common use for these blocks has been in the construction of residential basements, where the gray blocks are laid up with mortar between the blocks to form the walls of such basements. However, the outside exposed walls formed by such blocks are visually plain and unattractive.
Architectural concrete masonry blocks and retaining wall blocks are available in a variety of shapes, sizes, colors and textures. One way to enhance the visual appearance of such concrete blocks is to make the front face less uniform and more “natural” appearing. This can be done by using a splitting process to create an irregular front face, often referred to as a “rock-face”, on the block. In this process, as it is commonly practiced, a relatively large concrete workpiece which has been adequately cured is split to form two or more relatively smaller blocks. The resulting blocks have faces that are somewhat textured and irregular along the plane(s) of splitting. This process of splitting a workpiece into two or more blocks to create an irregular rock-like appearance on the exposed faces of the blocks is shown, for example, in Besser's U.S. Pat. No. 1,534,353, which discloses the manual splitting of blocks using a hammer and chisel.
Automated equipment to split a concrete workpiece to form blocks is well-known, and generally includes a splitting apparatus comprising a supporting table and opposed, mechanically-actuated or hydraulically-actuated, top and bottom splitting blades. A splitting blade in this application is typically a substantial steel plate that is tapered to a relatively narrow, or “sharp”, knife edge. A blade typically comprises one or more straight segments—although the blade segments can be curved as well—, with the top and bottom blades being mirror images of one another. The blades typically are arranged so that the knife edge of the top blade will engage the top surface of the workpiece, and the knife edge of the bottom blade will engage the bottom surface of the workpiece, with the blades aligned and perpendicular to the top and bottom surfaces of the workpiece. In operation, the workpiece is moved onto the supporting table and between the blades. The blades are brought into engagement with the top and bottom surfaces of the workpiece. An increasing force is exerted on each blade, urging the blades towards each other. As the forces on the blades are increased, the workpiece splits, generally along a vertical surface in alignment with the blades.
These machines are useful for the high-speed processing of blocks. They produce a somewhat irregular, “rock-face” or “split-face” finish on the blocks. No two faces resulting from this process are identical, so the blocks are more natural in appearance than standard, non-split blocks. However, the edges of the faces resulting from the industry-standard splitting process are generally well-defined, i.e., more or less regular and “sharp”. These blocks can be made to look more natural if the regular, sharp edges of their faces are eliminated.
One known process for eliminating the sharp edges on concrete blocks is the process known as tumbling. In this process, a relatively large number of blocks are loaded into a drum which is rotated around a generally horizontal axis. The blocks bang against each other, knocking off the sharp edges, and also chipping and scarring the edges and faces of the blocks. The process has been commonly used to produce a weathered, “used” look to concrete paving stones. These paving stones are typically relatively small blocks of concrete. A common size is 3.75 inches wide by 7.75 inches long by 2.5 inches thick, with a weight of about 6 pounds.
There are several drawbacks to the use of the tumbling process. In general, tumbling is a costly process. The blocks must be very strong before they can be tumbled. Typically, the blocks must sit for several weeks after they have been formed to gain adequate strength needed for the tumbling process. This means they must be assembled into cubes, typically on wooden pallets, and transported away from the production line for the necessary storage time. They must then be transported to the tumbler, depalletized, processed through the tumbler, and recubed and repalletized. All of this “off-line” processing is expensive. Additionally, there can be substantial spoilage of blocks that break apart in the tumbler. This is especially a factor if the blocks to be tumbled include integral concrete locator features, or if the blocks include relative thin webs (as is typically the case with architectural masonry units) that can crack during the tumbling process. Tumbling can also result in the edges of the block, although no longer sharp, being very regular. The tumbling apparatus itself can be quite expensive and a high maintenance item.
Another option for eliminating the sharp, regular edges and for creating an irregular face on a concrete block is to use a hammer mill-type machine. In this type of machine, rotating hammers or other tools attack the face of the block to chip away pieces of it. These types of machines are typically expensive, and require space on the production line that is often not available in block plants, especially older plants. This option can also slow down production if it is done “in line”, because the process can only move as fast as the hammer mill can operate on each block, and the blocks typically need to be manipulated, e.g. flipped over and/or rotated, to attack all of their edges. If the hammer mill-type process is done off-line, it creates many of the inefficiencies described above with respect to tumbling.
Yet another option for creating a more natural block face appearance and eliminating the sharp, regular edges of concrete blocks is disclosed in commonly assigned, copending U.S. patent application Ser. No. 09/884,795 (filed Jun. 19, 2001), and Ser. No. 09/691,864 (filed Oct. 19, 2000), and in U.S. Pat. No. 6,321,740, which are incorporated herein by reference in their entirety. As disclosed in these documents, a splitting assembly is provided with a plurality of projections that are positioned to engage the workpiece adjacent what will be the front face of the resulting block to create an irregular front surface and an irregular upper or lower front edge on the resulting block.
As disclosed in U.S. patent application Ser. No. 10/103,155 (filed Mar. 20, 2002), and Ser. No. 10/411,453 (filed Apr. 10, 2003), smaller projections in the form of a multiplicity of small peaks can be used in place of, or to supplement the action of, the larger projections mentioned in the preceding paragraph to eliminate the sharp, regular edges of concrete blocks. As described in these two applications, the peaks are positioned to engage the workpiece adjacent what will be the front face of the resulting block to help create an irregular upper or lower front edge on the resulting block. The left and right front edges are not generally affected by the peaks and tend to remain somewhat regular. However, in many applications, including masonry blocks and retaining wall blocks, the left and right side edges are also visible edges during use of the blocks, and it would be advantageous to eliminate the sharp regularity of the left and right side edges in addition to the upper and lower front edges.
Accordingly, there is a need for equipment and a process that can create irregular edges on all of the edges of a concrete block front face. The results should be achieved in a manner that does not slow down the production line, does not add costly equipment to the line, does not require additional space on a production line, and is not labor-intensive.